A NEW SPECIES OF CANCROID CRAB FROM THE PLIOCENE OF CALIFORNIA

Transcription

1 21 L I00 A / /. A NEW SPECIES OF CANCROID CRAB FROM THE PLIOCENE OF CALIFORNIA BY J. DALE NATIONS Reprinted from JOURNAL OF PALEONTOLOGY Vol. 42, No. 1, January, 1968

2 JOURNAL OF PALEONTOLOGY, V. 42 PLATE 10 J. D. Nations

3 JOURNAL OF PALEONTOLOGY, V. 42, NO. 1, p , PL. 10, JANUARY 1968 A NEW SPECIES OF CANCROID CRAB FROM THE PLIOCENE OF CALIFORNIA J. DALE NATIONS Museum of Paleontology, University of California, Berkeley ABSTRACT A new cancroid crab, Cancer davidi n. sp., is described from the middle Pliocene Etchegoin Formation of Kettleman Hills, California. It shows affinities with the Pleistocene to Recent Cancer gracilis Dana of the west coast of North America and is probably ancestral to it. A brief summary of fossil species of Cancer from the West Coast is given. Cancer davidi was associated with Anadara, Forreria, Kelletia and Trachycardium, genera which are characteristic of intertidal to sublittoral depths in areas where the minimum average surface temperature (February) is 13 C. or higher. Salinity of 20 ppm, or above, is indicated by the presence of Dendraster. INTRODUCTION FAIRLY complete carapace of a crab was collected by the author from the Patinopecten A "zone" (Woodring, et al., 1941) of the Etchegoin Formation (middle Pliocene) in the Kettleman Hills area, California. It was found in a fine- to medium-grained quartzose sandstone and was closely associated with the following species: Pelecypods: Glycimeris grewingki Dall Patinopecten lohri (Hertlein) Pseudocardium densatum (Conrad) Cirriped:. Balanus gregarius (Conrad) Echinoid: Dendraster gibbsii (Rémond) The specimen is well preserved, consisting of about two-thirds of the carapace plus the carpus and manus of the left cheliped. The missing third of the carapace, the right postero-lateral portion, is represented by an internal mold. The merus and the portions of the fixed and movable fingers beyond the first cutting tooth of the left cheliped are missing. No other appendages are preserved. The specimen was compared with Recent specimens of various species of Cancer in the collections of the Allan Hancock Foundation, University of Southern California, Los Angeles, California. Dr. John S. Garth of that institution generously granted access to the collections. He and Miss Janet Haig, Research Assistant at the Foundation, read the original manuscript and offered many helpful suggestions. The writer's appreciation is also due to Dr. J. Wyatt Durham of the Department of Paleontology, University of California at Berkeley, for advice and critical reading of the manuscript, and to Mr. Joseph H. Peck of the Museum of Paleontology, University of California (Berkeley), for assistance in photographing the specimens. SYSTEMATIC DESCRIPTION Family CANCRIDAE Alcock Genus CANCER Linnaeus "" CANCER DAVIDI, n. sp. PI. 10, figs. 1,2,4,5,7,10 Carapace. Carapace broadly oval, moderately convex, very slightly aerolated and densely granulated. Fronto-orbital border about onethird the width of carapace; with five teeth, the outer pair forming the inner angles of the orbits EXPLANATION OF PLATE 10 FIGS. 1,2,4,5,7,10 Cancer davidi new species. UCMP no. 37,889. 1, Dorsal view of carapace, Xl.S; 2, ventral view of carapace, X1-5; 4, chela and carpus, dorsal view, X2*0; 5, chela and carpus, inner side, X2.0; 7, anterior view, Xl-5; 10, chela and carpus, outer side, X2.0. From middle Pliocene Etchegoin Formation, Kettleman Hills, Calif. 3,6,8,9 Cancer gracilis Dana. UCMP no. 37,883. 3, Dorsal view of carapace, XI.5; 6, anterior view, Xl-5; 8, chela and carpus, inner side, X2.0; 9, chela and carpus, X2.0. Recent, Monterey Bay, Calif. 33

4 34 J. DALE NATIONS and the three median teeth extending more anteriorly than the other two. Orbits small (3.5 mm in diameter) with two fissures in each dorsal and ventral margin; inner angles more produced anteriorly than the outer ones. Antero-lateral margin of carapace slightly indented at closed fissures separating the teeth; evenly beaded with granulations approximately two or three times as large as those on the dorsal surface, but less than half the size of those on the margin of Cancer gracilis Dana. Antero-lateral teeth sub-truncate with a small granulated tubercle which is usually located one-third the distance from the anterior fissure of each tooth. Four left and two right antero-lateral teeth preserved. The first tooth. with its prominent granulated tubercle forming the outer angle of the orbit, is two-thirds the width of the others. Second, third and fourth teeth of equal width; with a prominent granulated tubercle one-third the distance back from the anterior fissure bordering each tooth. Carpus. Upper surface of carpus bounded by a band of coarse granules. Three high granulated tubercles on upper surface, one near the articulation with the manus and the other two arranged transversely about one-third the length of the carpus from the anterior end. The tubercle nearest the lower margin is on an elevated, granulated carina which extends nearly the length of the carpus. This closely resembles the carpus of C. gracilis except that the spines are lacking. Manus. Outer surface with six distinct and one less distinct longitudinal, beaded carinae. Upper one with two short spines, one at the upper-distal angle and one slightly anterior of the middle of the upper margin; also with a small pustulose elevation midway between the latter spine and the posterior end of the manus at about the point of downward curvature of the upper margin. Second carina (from the upper margin of manus) with four prominent granulated tubercles equally spaced along its length; the largest, most proximal tubercle terminates the carina just above the articulation with the carpus. A prominent pustule is located one millimeter proximally from each of the two middle tubercles. The third carina originates at the articulation with the dactylus and extends proximally only one-third the length of the manus. The fourth, fifth, sixth and seventh carinae are evenly beaded and distinct, with the sixth and seventh continuing onto the surface of the fixed finger. Inner surface of manus smooth with faint, evenly distributed granulations. Movable finger. Incomplete, broken anteriorly just beyond the first cutting tooth which consists of two sub-equal, conical cusps that are joined in a common base. The more distal cusp is slightly elongate due to the presence of a subsidiary cusp on its distal side. The cutting teeth are darker brown and appear to be more dense than the skeletal material in which they are set. The outer and inner surfaces of the finger are uniformly granulated. Fixed finger. Incomplete, broken anteriorly just beyond the first cutting tooth which is a small conical structure of the same material as those on the fixed finger. Holotype. University of California Museum of Paleontology collections (UCMP no. 37,889). Incomplete carapace plus the carpus and manus (less distal part of fixed and movable fingers) of the left cheliped. Type locality. La Cima, California: USGS 7.5' Quadrangle, scale 1:24,000, 1963; T. 22 S. R. 18 E., on boundary between sees. 16 and 17, about 1800 feet from south line of sections. Specimen collected on north side and near bottom of a branch of Arroyo Doblegado. UCMP invertebrate locality D Discussion. The marked overall similarity between Cancer davidi n.sp. and,recent individuals of Cancer gracilis Dana indicates that they are closely related. Such features as the shape of the carapace, character of fronto-orbital region, and the shape and position of ântero-lateral teeth suggest that the fossil might be referred to the species C. gracilis. However two distinct and diagnostic differences are exhibited by the cheliped of C. davidi which preclude its referral to C. gracilis. These are: absence of spines on the upper-distal and inner angles of the carpus (pi. 10, fig. 4, 5, 8, 9, 10) and the presence of two small, conical cutting teeth on the movable finger of C. davidi in the same position as a single, large, bulbous tooth on the movable finger of C. gracilis (pi. 10, figs. 5, 8). The carpus of C. davidi clearly shows a well preserved beaded carina on the distal angle and demonstrates conclusively that the absence of spines is not due to erosion (pi. 10, fig. 4). The two small cutting teeth on the movable finger of C. davidi arise from a common base which occupies the same position as the large cutting tooth in C. gracilis and strongly suggests that they are homologous structures (pi. 10, figs. 5, 8). In addition to the above-mentioned differences in the chelipeds, several less diagnostic differences may be noted. Comparison with a similar size specimen of C. gracilis (see table 1) shows that C. davidi has: 1) lower medial areolations with resultant lower convexity of the carapace, 2) carapace less expanded laterally, 3) anterolateral teeth less advanced and less pointed, 4) orbits at a lower level relative to antero-lateral

5 CANCROID CRAB FROM PLIOCENE OF CALIFORNIA 35 TABLE 1 Comparison of Cancer davidi n. sp. with Cancer gracilis Dana. Carapace: Length Width Height above central median tooth Texture Fronto-orbital region: Width Position of orbits Cancer davidi 35 mm 47 mm (estimated) 4.7 mm Densely and uniformly granular. 17 mm Lower margin of orbits at level of antero-lateral margins. 35 mm 51 mm Cancer gracilis 8.0 mm: variable, increasing with maturity. Densely granular, coarser on elevated portions. 17 mm Lower margin of orbits above level of antero-lateral margins. Antero-lateral teeth: Sub-truncate, with a small, granulated tubercle \ distance from anterior fissure of each tooth. Only 6 preserved. Low, project less than f length of base, small spine at anterior angle. Typically 9 teeth. Cheliped: Carpus Lacks spines on upper and inner-distal angles, otherwise identical with that of C. gracilis. Height 9 mm. Length of upper margin 12.5 mm. Two spines, one on upper-distal angle and one on inner angle. Height 9 mm. Length of upper margin 14 mm. M anus Similar to C. gracilis except upper two carinae more spinulose; upper margin curves downward more abruptly at proximal end. Height 12 mm. Length of upper margin 8 mm. Outer surface with seven longitudinal, beaded carinae, the upper two spinulose. Height- 13 mm. Length of upper margin 9.5 mm. Movable finger First cutting tooth divided into two small, sharp, conical cusps mounted on a common base. First. cutting tooth large, massive and elongate (2 mm long). margins, 5) tubercles on the superior surface of manus more prominent, and 7) frontal region produced farther anteriorly beyond the outer angles of the orbits. The total number of antero-lateral teeth on C. davidi cannot be determined because only six are preserved. The position and width of those six teeth are nearly identical with the corresponding six teeth in C. gracilis. Cancer gracilis is typified by nine antero-lateral teeth which are of unequal width and not spiny pointed. Based primarily upon the above mentioned differences in the carpus and movable finger between the fossil and the most similar living species, Cancer gracilis, the fossil is assigned to a new species Cancer davidi. This differentiation from C. gracilis is further supported by the differences designated as 1) through 7) in the discussion above. Cancer davidi has been compared with illustrations or the holotypes of all other known fossil species of Cancer from the West Coast and differs from all of them. Those species and their geologic ranges are listed below: Cancer anthonyi Rathbun Pleistocene-Recent Cancer branneri Rathbun Pleistocene-Recent Cancer gracilis Dana Pleistocene-Recent Cancer jordani Rathbun Pleistocene-Recent Cancer magister Dana Pleistocene-Recent Cancer productus Randall PI iocene-recent Cancer fissus Rathbun Pliocene Cancer granti Rathbun Pliocene Cancer urbanus Rathbun Pliocene Cancer bainbridgensis Rathbun Oligocène Cancer gabbi Rathbun Eocene Three of the species listed above are similar enough for possible confusion with C. davidi. Cancer gracilis is compared elsewhere in this paper. Cancer fissus differs by the unequal widths of the second, third and fourth anterolateral teeth, the deeper indentations in the margin between the teeth, the lack of a granulated tubercle on each tooth. Cancer granti differs by the serrated, upturned antero-lateral teeth of which the second, third and fourth are unequal in width. The close similarity between Cancer davidi and Cancer gracilis is interpreted by the writer as evidence of close genetic relationship between the two species. This similarity, in addition to

6 36 J. DALE NATIONS the stratigraphically lower occurrence of C. davidi than that of C. gracilis, whose oldest reported occurrence is Pleistocene (Rathbun, 1926), suggests that C. davidi is ancestral to C. gracilis. The differences between the two species can be attributed to evolutionary changes that have occurred during the three to five million year interval (Evernden, et al., 1964) from middle Pliocene to Pleistocene. ECOLOGY AND PALEOECOLOGY Cancer gracilis is known from Kasaan Bay, Prince of Wales Island, Alaska, to Playa Maria Bay, Lower California (Rathbun, 1931). However it is reported to be uncommon south of Point Conception, California (Menzies, 1951). Its bathymétrie range is intertidal to 56 fathoms (Rathbun, 1930). Cancer gracilis in San Francisco Bay occurs most abundantly at depths less than 12 fathoms and in areas of predominantly muddy bottom (Schmitt, 1921). It is also reported to occur in other shallow-water bay localities having a sandy bottom, often occurring where Cancer magister is abundant (Menzies, 1951). The temperature range in San Francisco Bay within which C. gracilis lives is from 8.8 C to 15.9 C, and in water with a salinity not less than 21.3 ppm (Schmitt, 1921). The minimum average surface temperature (February) of the ocean in the San Francisco Bay is about 11 C to 12 C (Durham, 1950). Cancer davidi was collected from a light-gray, medium-grained quartzose sandstone within the Patinopecten "zone" of the Etchegoin Formation. A paleoecological analysis of the faunal assemblage, from this "zone" indicates that the minimum average surface temperature of the sea during the time of deposition (Middle Pliocene) was at least 13 C. This is based on the occurrence of Anadara, Forreria, Kelletia and Tr achy car dium, which live only in waters with minimum average surface temperature higher than 13 C (Keen, 1963). The reportedly rare occurrences of Cancer gracilis south of Point Conception, California, where the minimum average surface water temperature (February) is 13 C (Durham, 1950) indicates that the species prefers cooler temperatures than those which existed in the type locality of Cancer davidi. This could mean either than C. davidi preferred warmer water than C. gracilis or that the two species were adapted to similar temperature ranges and that the optimum temperature for C. davidi would have been farther north during the middle Pliocene. The salinity of the environment must have been "normal" marine because all known living species of Cancer are exclusively marine (Mac- Kay, 1943), as is the genus Dendraster of which the species D. gibbsii was found in association with Cancer davidi. All available records of Dendraster indicate that the genus lives only in water with salinity above 20 ppm (J. W. Durham, personal communication, 1967). The faunal assemblage with C. davidi indicates that the depth of water was not greater than 75 fathoms because none of the genera mentioned above are found living below that depth (Keen, 1963). It is probable that the environment of deposition was between the littoral zone and 20 fathoms because these are the limits of occurrence of Kelletia, and all the genera mentioned are capable of ranging into the intertidal zone. REFERENCES DURHAM, J. W., 1950, Cenozoic marine climates of the Pacific coast: Geol. Soc. America Bull., v. 61, no. 11, p , 3 figs. EVERNDEN, J. F., SAVAGE, D. E., CURTIS, G. H., & JAMES, G. T., 1964, Potassium-Argon dates and the Cenozoic mammalian chronology of North America: Am. Jour. Sci., v. 262, p , 1 fig., tables 1-7. KEEN, A. M., 1963, Marine molluscan genera of western North America: Stanford Univ. Press, Stanford, Calif., 126 pages. MACKAY, D. C. G., 1943, Temperature and the world distribution of crabs of the genus Cancer: Ecology, v. 24, no. 1, p , 1fig.,2 tables. MENZIES, R. J., 1951, Pleistocene Brachyura from the Los Angeles area: Cancridae: Jour. Paleontology, v. 25, no. 2, p , 13 figs. RATHBUN, M. J., 1900, Synopses of North American invertebrates, VII, The cyclometopous or cancroid crabs of North America: Am. Naturalist, v. 34, p , 5 figs._, 1908, Descriptions of fossil crabs from California: U. S. Natl. Mus. Proc, v. 35, p , pis , 1926, The fossil stalk-eyed Crustacea of the Pacific slope of North America: U. S. Natl. Mus. Bull. 138, p , pis. 1-39, 5 figs., 1930, The cancroid crabs of America of the families Euryalidae, Portunidae, Atelecyclidae, Cancridae and Xanthidae: U. S. Natl. Mus. Bull. 152, p , pis , 85 figs., 1932, A new species of Cancer from the Pliocene of the Los Angeles basin: Jour. Wash. Acad. Sci., v. 22, no. 1, p. 19, 1 fig. SCHMITT, W. L., 1921, The marine decapod Crustacea of California: Univ. Calif. Publ., Zoology, v. 23, p , pis. 1-50, 165 figs. WOODRING, W. P., STEWART, RALPH, & RICHARDS, R. W., 1940, Geology of the Kettleman Hills Oil Field, California: U. S. Geol. Survey Prof. Paper 195, p , pis. 1-57, 15 figs. MANUSCRIPT RECEIVED MARCH 13, 1967